Fluorine contamination

Fig. 6. Top Morphology of FPL surface following fluorine contamination. This is to be compared to the standard FTL morphology of Fig. 14. Middle Climbing drum peel (CDP) strength as a function of F surface concentration. Bottom F concentration on FPL surfaces following doping the FPL etch solution and the rinse water with NaF. The dotted line corresponds to the surface concentration with which the CDP strength began to decrease. Adapted from Ref. [37].

In some cases, the degree of fluorine contamination of tantalum and niobium oxides containing increased fluorine levels is not very critical to the later application of the oxides. Applications related to the manufacturing of optic and electronic devices, however, require significant limitations of the fluorine content of tantalum and niobium oxides. 

Thus, in order to achieve precipitation of tantalum and niobium hydroxides with minimal levels of fluorine contamination, it is recommended to perform the process at a pH no lower than 10. 

Application of an excessive amount of ammonia solution in the precipitation of tantalum and niobium hydroxides from strip solutions usually ensures good quality of the products. Nevertheless, the method has two general problems. First, hydroxides containing low levels of fluorine contamination... 

Different procedures for the precipitation, washing and thermal treatment of hydroxides result in different fluorine contamination levels in the final products - tantalum and niobium oxides. Laboratory and industrial experience confirms some correlation between the initial concentration of fluorine in the dried hydroxides and the fluorine content in the final oxides obtained after appropriate thermal treatment. For instance, it is reported in [499] that if the initial concentration of fluorine in niobium hydroxide equals A%, then the fluorine content in the final niobium oxide can be estimated according to the thermal treatment temperature as follows ... 

Extensive work on the interaction of aromatic compounds with xenon difluoride has been carried out in order to investigate the reaction mechanism and the scope of the fluorination depending on the substituents electronic nature.26-59 62 It has been found that benzene and substituted aromatics react with xenon difluoride at room temperature in the presence of hydrogen fluoride to form the typical products of electrophilic fluorination contaminated with low quantities of difluoro-substituted molecules. 

Adhesion of polyimide to fluorine-contaminated SiOz surface. Effect of aminopropyltriethoxysilane on the adhesion... 

Abstract—The adhesion of pyromellitic dianhydride-oxydianiline (PMDA-ODA) polyimide to fluorine-contaminated silicon dioxide (F-SiO,) with y-aminopropyllriethoxysilane (APS) adhesion promoter has been studied as a function of the peel ambient humidity. The peel strength was not affected by the change in peel ambient relative humidity (RH) from 11-17% to 35-60% when APS was used at the interface. Without APS, the adhesion degraded significantly with this change in RH. It was found that although the dip application of APS caused the removal of about 80% of the initial atomic percentage of fluorine on the surface, it could not be totally removed even after several days in water at elevated temperature. 

Keywords Polyimide adhesion fluorine contamination aminosilane moisture effects. 

This work continues our initial study concerning the effect of fluorine contamination on PMDA-ODA adhesion [4], In this study we apply APS at the interface. We continue to use the peel test to monitor the adhesion and X-ray photoelectron spectroscopy (XPS) to study the surfaces and loci of failure after the peel test to elucidate the failure mechanisms. 

Fluorine contamination has been reported in various environments and applications in the past. It has shown up in plasma processing [10-18], as crosscontamination from storage in contaminated containers or with contaminated samples [14,18], and modification of aluminum deposited on fluoropolymer substrates and other polymers having fluorine-based plasma treatments has also been observed [19-21]. Fluorocarbon lubricants have also been noted to modify the oxide structures on aluminum alloys [22,23], and the degradation of AI2O3 catalytic supports has been associated with fluoride conversion during reactions with fluorocarbons [24]. Alloy oxide modification has also been well noted in the presence of fluorine compounds not of the fluorocarbon family [25]. 

Most of these discussions regarding fluorine contamination of aluminum surfaces have focused on the conversion of aluminum oxide to fluoride or oxyfluoride. Evidence for similar conversions was included, and in extreme cases conversion to aluminum bonding quite similar to that in AIF3 was found. However, the poor adhesion of the samples skipping the O2 plasma treatment is related not to the fluorine contamination as such, but rather to the carbonaceous nature of the adsorbed materials, which is subjected to the plasma polymerization of TMS. Oxygen plasma cleaning removes this carbonaceous component, while the surface fluorine concentration is enhanced. 

Figure 10.12 FIs and C Is spectra from both alloy panels and Si wafer pieces attached to them. Top figure panels are from samples exposed to the evacuation process and bottom panels are from samples exposed to the O2 plasma cleaning process. The third trace in each of the bottom panels is from an alloy panel that was O2 plasma cleaned in a new reactor with minimal fluorine contamination, indicating that the high binding energy C Is peak is not associated with fluorocarbon bonding.

Figure 10.14 The decay of fluorine contamination with continued reactor use, involving multiple intermittent chamber evacuations and O2 and Ar plasma-treatments of new substrates other than this intermittent use and times when chamber-cleaning procedures were employed, the reactor is continually under vacuum, indicating that this contamination does gradually pump out.

XPS studies on the panels prepared with the HFE line disconnected, the liquid N2 trap, and the vacuum pump oil change confirmed that these are not possible sources of fluorine contamination. The F content gradually decreases with the evacuation time and intermittent O2 plasma discharges. 

Fluorine contamination of the reactor wall is clearly evident. Air plasma treatment introduced a small but clearly identifiable amount of F on the treated surface. 

Since it was observed that fluorine contamination was a possibility and had potentially detrimental effects as described in Chapter 10, the excellent primer adhesion achieved with Tfs/(Ar) and Tcs/(Ar), shown in Table 31.3, has significant importance in the practical application of the plasma technique without any of the potentially deleterious effects of fluorine-based systems. Argon plasma treatments on both flow system TMS (Tfs) and closed system TMS (Tcs) polymers were then investigated as an additional system modification that could provide strong adhesion without the incorporation of fluorine-containing monomers in the quest to produce chromate-free coatings systems. 

Kim D-H, Jeon C-S, Baek K, Ko S-H, Yang J-S. (2009). Electrokinetic remediation of fluorine-contaminated soil Conditioning of anolyte. Journal of Hazardous Materials 161 565-569. 

In cases in which surface treatment produces a smooth oxide (intentionally or unintentionally) bond performance is controlled by chemical bonds across the oxide-epoxy interface. This situation can arise, for example, when an FPL adherend is rinsed in fluorine-contaminated water or is exposed to fluorine vapor. ( 8) The oxide-epoxy bonds are relatively weak and are readily disrupted by moisture.(, 50) As a result, bond failure is rapid upon exposure to humid conditions, and the crack propagates along the adhesive-oxide interface. In cases in which a smooth oxide is formed intentionally, coupling agents such as silanes can be used to improve durability. This is discussed in detail in Chapter 9 by E. Pleuddemann in the accompanying volume, Fundamentals of Adhesion. 

Figure 4.9 Effect of residual fluorinated contamination remaining on the surface of a carbon fibre composite after removal of the peel-ply on the subsequent joint strength [61].

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